1. Field of the Invention
The present invention relates to devices for controlling brake fluid pressure used, for example, in an anti-lock brake system (ABS) and other like systems.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2000-52959 teaches a device for controlling brake fluid pressure comprising a plunger pump and a motor for driving the plunger pump. The plunger pump transfers brake fluid from a wheel cylinder into a reservoir provided in the body of the device for controlling brake fluid pressure. The plunger pump refluxes the brake fluid previously introduced into the reservoir to the side of the master cylinder. The plunger pump and the output shaft of the drive motor are coupled together to transmit power in a motor cam chamber provided in the body of the device for controlling brake fluid pressure. Further, there is a drain passage formed for draining the brake fluid seeping (leaking) by the plunger pump. The drain passage connects the motor cam chamber to the exterior. This device is additionally provided with a valve located in the drain passage in order to drain the brake fluid that seeped into the motor cam chamber and to prevent a sudden infiltration of water from the external environment. By using this device for controlling brake fluid pressure, the brake fluid that seeped into the motor cam chamber is drained through the drain passage, thereby preventing the grease of the bearing supporting the output shaft of the drive motor from being washed away by the brake fluid. Consequently, the draining of brake fluid from the motor cam chamber aids in preventing the bearing from being prematurely worn due to the depletion of grease and also aids in preventing the shortening of the life of the product. In addition, the valve provided in the drain passage prevents water from infiltrating into the drain passage when the device is submerged under water, for example.
However, though a sudden infiltration of water into the drain passage can be prevented, this device for controlling brake fluid pressure is not capable of completely preventing a relatively slow intake of water. For example, when the car is washed after having stopped the engine, the temperature in the motor cam chamber drops and the pressure therein decreases, causing water to be drawn into the motor cam chamber of the device for controlling brake fluid pressure.